View SlideshowRequest to buy this photoDOUG MURRAY | ASSOCIATED PRESSTotal lunar eclipses, such as this one seen from Florida in 2004, are
not that rare. Four in a row, however, are something special. Starting Tuesday,
four total eclipses will be seen — one every six months.

Scientists who study deep space and string theory usually don’t get that worked up over lunar
eclipses.

“Most of them are busy studying galaxies and quasars and the Big Bang,” said Fred Espenak, 62, a
retired astrophysicist who now lives in Arizona.

“In this day and age, they aren’t very much use in terms of science.”

Then again, come Tuesday, Espenak will head outside in the early morning and take in a spectacle
he spent a career predicting.

That’s when Earth will block the sun’s light from reflecting off the moon, causing a total
eclipse — the first of four that will occur every six months. The event is called a “tetrad.”

“They’re a beautiful, natural phenomenon,” said Espenak, 62, who used to work at the NASA
Goddard Space Center in Maryland. “And you don’t even have to be out in the dark country — you can
be in the middle of the city.”

For people in academia, the tetrad will be a way to “get lay people to speak with scientists —
sort of an outreach opportunity,” said David C. Ingram, chairman of Ohio University’s physics and
astronomy department.

The first begins just before 2 a.m. on Tuesday. But the real show, weather permitting, peaks
about an hour later. That’s when Earth’s shadow, or umbra, will entirely block the sun’s rays from
illuminating the moon.

Light rays that bend around Earth’s edges will give the moon an eerie, reddish glow. That’s why
it’s called a “blood moon.”

“The moon can have variations of this hue depending on Earth’s atmospheric conditions at the
time,” said Joe Renzetti, the president of the Columbus Astronomical Society. “The more humidity or
particulate matter, the darker the hue. Occasionally, a lunar eclipse can appear brown or
blue."

An even better show would be looking at Earth from the moon. The planet would appear to have a
ring of fire, representing every sunrise and sunset around the world — simultaneously.

“Over the centuries, it has been extraordinary. There is something quite awe-inspiring about
seeing the moon slowly disappear from the sky and then turn a bloody red,” said Tom Burns, the
director of Perkins Observatory in Delaware County.

“You really get a sense of standing on the African savannah and seeing the moon being swallowed
up by a beast.”

Some ancient cultures took the event as a bad omen.

“Before people knew what was going on, lunar eclipses scared people out of their wits that the
world was going to end,” said Alan MacRobert, senior editor at
Sky & Telescope magazine.

“People would go out and bang pots and pans, shoot arrows at the moon to scare whatever evil
thing was possessing the moon. And it always worked,” MacRobert said. “The moon always
reappeared."

The precision with which eclipses occur doesn’t require super-computing power, he said. “
Gravitational effects in frictionless space are very linear. ... You can calculate them with very
high accuracy, very far in the future.”

The tetrad will have a potentially huge audience — the entire dark half of Earth. And you’ll
need no more than your eyes to appreciate it.

“If you were on the phone with someone in Hawaii, you would be able to see it at the same time,”
Burns said, although Hawaiians won’t need to stay awake much past midnight.

“This is one of the coolest naked-eye events,” MacRobert said, even if it’s not rare.

In the 5,000 years between 1999 B.C. and 3000, there will have been 3,479 total lunar eclipses,
according to NASA research. Of those, 568 eclipses will include 142 tetrads.

The last tetrad occurred in 2003-04. The next one will take place in 2032-33.

The complexity of predicting tetrads relates to small changes in Earth’s elliptical orbit around
the sun, Espenak said.

In about 500,000 years, when Earth’s orbit is circular, “alignments will be such that we just
won’t have tetrads,” he said. But slowly — very slowly — they will begin to reoccur.

“This is a chance to go out into nature and see some of the cycles of the cosmos taking place
before your eyes,” MacRobert said.. “It takes us out of our own little world.”

Burns agrees.

“Even though you know exactly why it’s happening,” he said, “there’s something about the
experience that at least for a moment lets you forget the science and experience the fear and the
awe that people must have experienced long ago.”